The present invention relates to treatment fluids that are suitable for use in subterranean operations. Among their many benefits, the treatment fluids provide compatible biocide and friction reducing treating effects in a subterranean treatment fluid in a subterranean operation such as a drilling, completion, or stimulation operation. Associated methods are also disclosed.
When treatment fluids utilized in drilling or stimulating oil or gas wells contain an undesirable bioburden, those fluids when introduced into a subterranean formation can undesirably contaminate the subterranean formation. As used herein, the term “bioburden” refers to the bacteria that exist as members of a biofilm, a meta-community consisting of microbial cells (algal, fungal or bacterial) and the extracellular biopolymers the cells produce in a water system. An example of what might be considered an undesirable bioburden may be the presence of bacterial slime which plugs permeability flow paths, impairing the production of oil and gas from subterranean formations. Also, bacterial action or the bi-products of their activity (e.g., hydrogen sulfide production), which may corrode production or transport piping, may be considered an undesirable bioburden. As used herein, the term “treatment fluid” refers to any fluid that may be used in a subterranean application in conjunction with a desired function and/or for a desired purpose. The term “treatment fluid” does not imply any particular action by the fluid or any component thereof.
Anaerobic bacteria and particularly sulfate reducing bacteria (SRB), present in the fluid can lead to a variety of undesirable outcomes if introduced into the subterranean formation. For instance, once in the formation, if the bacteria produce sludge or slime, they can cause a reduction in the porosity of the formation, which in turn is thought to reduce the production of oil and/or gas therefrom. Additionally, sulfate reducing bacteria produce hydrogen sulfide, which, even in small quantities, causes many problems. For instance, the presence of hydrogen sulfide in produced oil and gas can cause excessive corrosion in metal tubular goods and surface equipment, damage to treating chemicals lowering their effectiveness, a lower oil selling price, and a necessity to remove hydrogen sulfide from gas prior to sale.
When a formation that has been fractured becomes overly contaminated with bacteria, e.g., by the introduction of bacteria through the fracturing fluid used during the fracturing treatment, or through other fluids such as drilling fluids, workover fluids, and kill fluids, the presence of the bacteria can be particularly problematic. In some instances, the bacteria can be long distances from the well bore as a result of having been carried into fractures in the formation by the fracturing fluid. Combating the bacteria in such formations often proves to be difficult. For instance, oftentimes the bactericide cannot reach the bacteria in these fractures. Thus, the bactericide cannot reach the bacteria. Additionally, the proppant materials in the previously formed fractures may be disturbed, thereby reducing the permeability of the formation.
In order to effectively treat water against bacterial contamination, a fast acting biocide is needed. This may be even more important for on-the-fly treatments, where biocides have a very short contact time with the water before other treating chemicals are added and the fluids are pumped down hole. To get an effective fast kill of bacteria, in some instances it is believed to be helpful to include a biocide enhancer to aid the biocide treatments or work synergistically with the biocide. Specific classes of chemicals which accomplish this may be quaternary surfactants. “19N™,” a cationic surfactant commercially available from Halliburton Energy Services, Inc., Duncan, Okla., is an example of a biocide enhancer that may be suitable. When used in combination with biocides such as sodium hypochlorite or glutaraldehyde, in some instances, bacterial problems may be treated in a little as 5 minutes. The term “fast kill” as used herein refers to kill time of 5 minutes or less.
Although quaternary surfactants can be useful when use in conjunction with biocides, some quaternary surfactants may have a fundamental incompatibility with anionic friction reducers, which are also useful in subterranean operations. Although the exact theory is unknown, it is believed that this fundamental incompatibility may be due to the formal charges present on both molecules that may cause the quaternary surfactant and the friction reducer to react and form a precipitant. Additionally, some biocides (such as oxidizers) may degrade the friction reducer. This is viewed as disadvantageous because if the friction reducer degrades or settles out of the solution, the fluid may require a great deal of pressure during pumping, which can lead to safety concerns and inefficient treatments.